HOW DISCOVERIES ARE MADE 127 



set them in rapid vibration ; and they may even break up 

 molecules and cause them to assume other forms of 

 combination. And in doing so, very short electric waves 

 are sent out through the ether, and these are what we 

 term ' light/ and ' radiant ' heat. 



There are several other lines of evidence which support 

 this notion. For example, a pure gas cannot be heated 

 red-hot or made to glow by heat alone. There must be a 

 chemical change of some kind at the same time. Again, 

 a Welsbach incandescent gas mantle, if made of pure 

 thoria (and that means ' nearly pure,' because we are not 

 acquainted with really pure substances), does not give out 

 much light when heated, but if some other earth, such as 

 oxide of cerium, is mixed with the thoria, the familiar 

 brilliant incandescence is produced when it is heated by a 

 Bunsen burner. The ' pencil ' of a Nernst lamp is made 

 chiefly of zirconia, another earth ; and here, again, unless 

 the zirconia is mixed with a trace of some other oxide, it 

 will not glow very brightly when a current of electricity 

 is passed through it. In all these cases there is almost 

 certainly chemical change, and also, no doubt, evolution of 

 corpuscles of electricity which set the ether vibrating and 

 so produce light and heat. 



It may be asked : ' Do substances not lose weight when 

 corpuscles are being shot out ? ' Professor Landolt, of 

 Berlin, has been making experiments on the gain or loss 

 of weight when a weighed quantity of substances capable 

 of chemical change are mixed in a closed vessel ; and he 

 finds that in many cases there is a minute loss of weight. 

 Perhaps that is due to the escape of corpuscles ; but too few 

 experiments have been made to allow of a definite answer. 1 



Perhaps, too, the corpuscles when expelled are not 

 moving very rapidly, and are thus absorbed by the sides 

 of the vessel in which the reaction takes place ; and this 



1 He has since shown that there is no change of weight. 



